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Journal of the Korean Society of Safety, Vol. 32, No. 2, pp. 27-33, April 2017 Copyright@2017 by The Korean Society of Safety (pissn 1738-3803, eissn 2383-9953) All right reserved. https://doi.org/10.14346/jkosos.2017.32.2.27 ETA 를통한연구실험실콘센트회로의전기재해분석 김두현 김성철 박종영 * 김상철 ** 충북대학교안전공학과 * 광주과학기술원 ** 세명대학교보건안전공학과 (2017. 1. 4. 접수 / 2017. 2. 7. 수정 / 2017. 4. 17. 채택 ) Analysis of Electrical Accident for Outlet Circuit of Laboratory on ETA Doo-Hyun Kim Sung-Chul Kim Jong-Young Park * Sang-Chul Kim ** Department of Safety Engineering, Chungbuk National University * Gwangju Institute of Science and Technology ** Department of Occupational Health and Safety Engineering, Semyung University (Received January 4, 2017 / Revised February 7, 2017 / Accepted April 17, 2017) Abstract : This study is intended to identify issues on the basis of investigating the actual state of laboratory environment and outlet circuit, and derive end states by expressing sequences from the initiating event of disaster to accident in leakage current, poor contact and overload through ETA(event tree analysis). To this end, this study investigated the actual state of electric equipment of laboratory at universities in all parts of country. And it is shown that most of them are failure in electric work and user negligence in the investigation of actual state. It is found that there is earth fault and defect in wire diameter in the failure of electric work and the problem of partial disconnection due to wire bundling and poor contact in user negligence. Outlet-related component, failure rate and initiating events are composed of a total of 41 initiating events, i.e., 30 internal initiating events and 11 external initiating events. And end states are composed of a total of 15 parts, i.e., 3 electric power parts and 12 safety parts. Earthing class 3 is the most important safety device against leakage current (initiating event). And in case of poor contact, it is necessary for manager to check thoroughly because there is no safety device. In case of overload/overcurrent, when high-capacity equipment is connected, a molded case circuit breaker, safety device, worked. However, in most cases, it is verified that this doesn't work. This study can be utilized as electric equipment safety guide for laboratory safety manager and managers. Key Words : outlet, laboratory investigation, leakage current, poor contact, overload, ETA(event tree analysis) 1. 서론 국내연구실점검 진단결과를바탕으로작성한 대학화재사고분석및실험 실습실안전사고사례집 (2010) 에의하면, 전국 87 개대학을대상으로분야별안전지적사항을조사한결과전기안전분야가전체지적건수의 28.7%(5,426 건 ) 로가장높게나타났다 1). 전기분야의지적건수가높은이유는연구실험실의연구원의대부분이전기비전문가들로구성되어있고, 연구와관련된다양한전기설비의유입 유출로인하여어떤설비를사용하고있는지를정확하게관리되지않아서발생된다고한다. 그러나연구실험실이든가정이든공장이든전기설비의설치는공통적인부분이많다. 건물이건축되고전기설비를설치할때옥내배선까지의 시설은전문가에의해서안전하게설치된다. 문제는콘센트와관련된배선 / 배선기구에서주로전기재해가발생한다. 한국전기안전공사에의하면감전의 80% 가상용전압 (220 V) 에발생하고있으며, 전기화재는콘센트를포함한배선 / 배선기구에서가장높게나타났다 2). 주요발생원인으로는전기공사실패와부주의이며, 전기공사의실패는접지불량, 전선굵기불량이며, 부주의는접촉불량, 고용량전열기사용 (3 kw이상 ), 전선의묽음처리, 부적절한이동형전기설비관리등이해당된다. 접지불량으로발생되는문제는감전과누전화재가발생되며전선굵기불량은차단기정격전류이하에서도과부하로인하여해당전선의용량을초래하는결과로화재가발생한다 3-4). 콘센트와플러그의접속불량의경우 5 A 의낮은전류임에도불구하고해당개소에 400 이상 Corresponding Author : Sung-Chul Kim, Tel : +82-43-267-2463, E-mail : ksc3650@naver.com Department of Safety Engineering, Chungbuk National University, Cheongju, Chungbuk 28644, Korea 27

김두현 김성철 박종영 김상철 의열이발생되며, 주위에가연물이있으면바로화재로이어진다 5). 고용량전열기기사용은콘센트의허용전류를초과하여콘센트의구조체인플라스틱을탄화시키는열에너지로작용한다 5-6). 상기와같이대부분의재해는 220 V 의상용전원에서콘센트와관련한배선 / 배선기구에서나타나고있지만재해건수를줄이지는못하고해마다증가하는추세이다. 현재의콘센트연구는전기화재로열발생과정을증명하는연구가대부분이며, 누전, 접촉불량, 과부하의초기사상혹은촉발사상 (initiating event) 으로부터재해사고까지의연쇄적전개를표현하고초기사상을바탕으로결과상황들을유도하고유도된결과상황들에대한체계적인관리방안연구는없는실정이다 6). 따라서본연구에서는콘센트와연계된전기회로를중심으로전기설비사고통계분석, 연구실관련법분석, 실태조사를바탕으로문제점들을분석하고사전의위험요소를찾고위험요소들을평가하고자한다. 분석기법으로는사건수목분석 (ETA, Event Tree Analysis) 을이용하였고, 누설전류, 접촉불량, 과부하에재해발생의초기사상으로부터재해사고까지의연쇄적전개를표현하여결과상황들을유도하였다 7). 본연구는연구실안전관리자및관리자들의전기설비안전지침서를활용가능하다. 2.1 전기설비의사고통계 2. 이론적배경 전기설비의사고는감전과전기화재로크게나눌수있다. 감전은 2011 년한국전기안전공사의저압설비에서총 242 건중가장높은곳은전로 ( 전기배선 ) 에서 75 Fig. 2. Number of electrical fire for electrical equipment and appliance(2011). Table 1. Number of electrical fire for wiring and wiring of appliance(2011) Equipments Classify Number of accidents Percentage(%) Wiring(HIV) 570 34.4 Cord and wiring of appliance 364 22.0 Outlet 298 18.0 Wiring(DV) 168 10.1 Power supply wiring 144 8.7 Multi-outlets 88 5.3 Plug 18 1.1 Socket 7 0.4 Total 1,657 100 Fig. 1. Number of electric shock for electrical equipments of low voltage(2011). 건, 콘센트에서 66 건, 차단기 17 건순으로나타났다. 콘센트는전기배선과연결되어있기때문에두건수를합하면 58% 로감전에대해서는이들설비를철저하게관리해야한다 1). 전기화재는기타및미상을제외한총 5800 건중에서배선및배선기구 (1,929 건 ) 에서의화재가가장높게나타났고다음으로전기설비순으로나타났다. 배선및배선기구에서는옥내배선 (570 건 ) 이가장높았고, 다음으로코드선 (364 건 ), 콘센트 (298 건 ) 로나타났다 1). 배선및배선기구에서콘센트회로와관련하여코드, 콘센트, 멀티탭및플러그를포함하면 46.8% 가나타난다 1). Fig. 1 은저전압전기설비에서의감전수를제시하였고 Fig. 2 는발화관련기기별화재건수를 Table 1 은배선및배선기구에서의전기화재건수를나타내었다. 28 J. Korean Soc. Saf., Vol. 32, No. 2, 2017

ETA 를통한연구실험실콘센트회로의전기재해분석 2.2 연구실관련법미래창조과학부는연구실안전점검및정밀안전진단에관한지침을고시했다 ( 미래창조과학부고시제 2013-109호 ) 8). 전기분야는 15개항목의점검항목을분류하였으며그중점내용은분전반, 고용량기기, 콘센트, 전기배선, 개인전열기, 방폭전기설비, 차단기및접지와관련된내용이다. 이중에서고용량기기단독회로구성, 콘센트문어발식접속, 전선피복노후및손상, 콘센트사용및관리상태등인데, 지침은산업안전보건기준에관한규칙, 실험실안전보건에관한지침, 전기설비기술기준의판단기준을근거하고있다. - 고용량기기단독회로구성 : 전기설비기술기준의판단기준제166조 ( 옥내전로의대지전압의제한 ) 를근거하여정격소비전력 3 kw이상의전기기계기구에전기를공급하기위한전로에는전용의개폐기및과전류차단기를시설하고그전로의옥내배선과직접접속하거나적정용량의전용콘센트를시설할것. ( 이하생략 ) - 전선피복노후및손상 : 산업안전보건기준에관한규칙제313조 ( 배선등의절연피복등 ) 와산업안전보건기준에관한규칙제315조 ( 통로바닥에서의전선등사용금지 ) - 콘센트사용및관리상태 : 전기설비기술기준의판단기준제170조 ( 옥내에시설하는저압용의배선기구의시설 ) 5 저압콘센트는제33조제2 항의경우를제외하고접지극이있는것을사용하여접지하여야한다. 다만, 주택의옥내전로에는제33조제2항의경우에도불구하고접지극이있는콘센트를사용하여접지하여야한다. 상기와같이고용량, 콘센트및전기배선의관리는철저하게그리고현행법에준해서관리되어야하지만실질적으로부적합하게관리하고있다. (5,426 건 ) 를차지했다 9). a) Ground not installed b) Ground not installed and thickness defect of wiring 2.3 실태조사 Fig. 3은연구실험실실태조사에따른문제점을나타낸것들이다. Fig. 3 a) 는접지선을시설하지않은것을나타내고있고, Fig. 3 b) 는접지선미설치와전선굵기불량을지적한내용이다. Fig. 3 c) 는고용량과관련하여 7,500 W를단독차단기또는단독콘센트를사용하지않았으며, 이로인하여해당콘센트에홀이탄화된것을볼수있다. 이런이유로국내연구실점검 진단결과를바탕으로작성한 대학화재사고분석및실험 실습실안전사고사례집 (2010) 에의하면, 전국 87개대학을대상으로분야별안전지적사항을조사한결과전기안전분야가전체지적건수의 28.7% c) High capacity usage(over 3 kw ) Fig. 3. Intellectual case of electrical installation for outlets at laboratory. 한국안전학회지, 제 32 권제 2 호, 2017 년 29

김두현 김성철 박종영 김상철 Fig. 4. Number of intellectual case at laboratory 9). 2.4 ETA 분석목적및방법 7) ETA( 사상수목분석, Event Tree Analysis) 기법은재해사고의발생과정을재해요인들의연쇄로파악하여, 재해발생의초기사상혹은촉발사상 (initiating event) 으로부터재해사고까지의연쇄적전개를나뭇가지형태로표현하는귀납적인시스템분석기법이다. 이렇게하면어떤과정을거쳐사고가발생하는지눈으로확인할수있다. 여기에다각재해발생요인들의발생확률까지알수있다면, 정성적인분석기법인동시에정량적인분석기법의장점도활용할수있는것이다. 원래이기법의원리는의사결정수목 (Decision Tree) 에서차용한것으로, 상호배반적인상황의전개와그발생확률을가시적으로확인할수있다는장점이있어, 종래에는재해의확대요인에대한분석등에이용되어 많은성과를올리고있다. 어떤사고에든여러가지재해발생요인들이연관되어있다. 이요인들을도표상단에왼쪽에서부터오른쪽으로차례대로나열한다. 이때가장왼쪽의요인은시스템에고장이나사고가발생하게되는부정적인사상, 다시말해사고의초기사상을기입하는것이보통이고, 오른쪽끝은시스템구성요소의상태조합에의한결과상황들 (End States) 이나열되는것이니까, 그중간의재해요인들은가급적시간경과에따라재해사고가전파되거나혹은확산되는데관계되는요인들을나열하도록한다. 재해초기사상이결정되었으면그점에서다음요소의발생사상에따라가지를나눈다. 이때성공사상, 다시말해시스템구성요소가정상적으로작동하는경우를맨윗가지에, 정상적으로작동하지못하는고장상태를맨아래가지에할당한다. 필요하다면다양한고장모드에따라그중간에여러개의가지를더만들수있다. 그다음단계에서는뻗어진가지의끝점에서, 또다시다음재해발생요소의성공, 실패에따라가지를나누어간다. 이렇게하여결과상황까지뻗어나가면, 시스템에발생할수있는모든상황들이오른쪽가지끝에나열되게된다. 3. 콘센트와연계된전기회로및구성부품분류연구실험실의대부분의콘센트는상용전원인 220V 를사용하고있으며, 계측기는물론이고전기설비들이접속되어다양한연구실험에사용된다. Fig. 5에서실험기자재의프레임은전원플러그의접지선과연결되어있으며콘센트의구리바 (E3, 3종접지 ) 와접속된다. 실험기자재의누전시에접지선을통하여귀로된전류에의하여누전차단기가감지하여전원을개방하게된 Fig. 5. The simplified electric power installation diagram showing the components considered in the analysis. 30 J. Korean Soc. Saf., Vol. 32, No. 2, 2017

ETA 를통한연구실험실콘센트회로의전기재해분석 다. 배선용차단기는과부하 / 과전류발생시, 또는단락시에전원을개방하여전기설비를보호한다. 콘센트회로는분전반, 전원플러그, 코드, 콘센트, 전기배선으로구성되어있다. 분전반에는배선용차단기와누전차단기접지바등이주요구성부품이이다. 전기배선은옥내배선 (HIV, Heat resistance in-door PVC wire), 인입선으로사용되는전선 (DV, PVC insulated drop wire), 전력용전선및접지선으로구성되어있다. 전력공급을안정적으로제공하는것이목적이기때문에전기내선규정에의거하여전기공사를실시한다. Fig. 5는콘센트와연계된회로를나타내었다. 4. 콘센트회로의초기사상및결과상황들 콘센트회로에대한고장률은프론티스의 PCT Windchill Quality Solutions 의데이터베이스를바탕으로하였고 11), 초기사상과결과상황들은한국전기안전공사 12) 와 IEEE gold book 13) 및전문가활용에서제시한기준을바탕으로하였다. 초기사상은콘센트의구성부품및회로에서나타날수있는내 외부에서발생가능한사상을제시하였고초기사상으로인하여콘센트전체에나타날수있는결과상황들 ( 전원관련 ES 와안전관련 ES) 을도출하였다. 초기사상은내부초기사상 30 개, 외부 11 개로총 41 개구성되어있으며, 환경적요소및휴먼에러도첨부하였다. 결과상황들은전력부분 3 개, 안전부분 12 개로총 15 개로구성하였다. Table 2 는콘센트회로에대한주요구성품, 고장률을제시하였다. 본고장률과비율은콘센트뿐만 (Fig. 5) 아니라일반전기설비의신뢰성을분석하는데중요한자료로활용할수있다. Table 3 은초기사상, Table 4 는결과상황들을나타내었다. Table 2. Components, failure rates of the outlet circuit Components Rack structure MCCB/ELB Connectors Switch Outlet Plug Cord and wiring of appliance Indoor wiring(hiv) Power supply wiring Failure rates 2.44E-05 6.80E-07 4.51E-07 1.15E-05 5.95E-05 3.20E-05 1.25E-06 1.05E-06 2.03E-06 Table 3. List of initiating events(ie) for components and overall circuit of the outlet circuit IE Internal IE Broken Binding/Sticking Intermittent operation Short Fused fusible disconnecting Flashover Malfunction Cut/Scarred/Punctured Worn Fails To Open Electrical Overstress Premature Open Degraded output Does not open Fails To Close Opens Without Command Stuck Open Mechanical damage Overvoltage Overcurrent Leakage Internal fire Excessive wear Improper output Poor contact Normal operation Function Failure Microcrack Parameter change Breaker Open without stimuli Flood Earthquake Animals(mainly cables, module junction box, ventilation holes) Lightning Sabotage(terrorism) Adversary action(vandalism) Explosion (considered for battery, inverter) External fire Mechanical shock(including module cleaning actions, ground-works affecting cables, structural damages to all electric components) IE_INT_BRO IE_INT_BS IE_INT_IO IE_INT_SHORT IE_INT_FFD IE_INT_FO IE_INT_MAL IE_INT_CSP IE_INT_WORM IE_INT_FTO IE_INT_EO IE_INT_PO IE_INT_DO IE_INT_DNO IE_INT_FTC IE_INT_OWC IE_INT_SO IE_INT_MEDAM IE_INT_OVERVLT IE_INT_OC IE_INT_LEAK IE_INT_FIRE IE_INT_EW IE_INT_IO IE_INT_PC P_INT_NOROPR IE_INT_FF IE_INT_MICRO IE_INT_PCB IE_INT_OWS IE_EXT_FLOOD IE_EXT_ERTQUAKE IE_EXT_ANIMAL IE_EXT_LIGHTN IE_EXT_SABOTG IE_EXT_ADVACT IE_EXT_EXPLSN IE_EXT_FIRE IE_EXT_MECHSHCK Wiring(DV) 1.27E-07 High humidity IE_EXT_HUMID Earthing wiring 1.62E-05 Human error IE_EXT_HUMAN 한국안전학회지, 제 32 권제 2 호, 2017 년 31

김두현 김성철 박종영 김상철 Table 4. List of End States(ES) for components and overall circuit of the outlet circuit ES Power-oriented ES Normal operation P_NO Complete success No power P_NP_F Failure Improper power (for voltage, current, frequency level) P_IP Failure Safety-oriented ES No power S_NP_S System safely shut-down, success Overheating S_OH Failure Open S_OPEN Failure Fire S_FIR Failure Electric shock S_ES Failure Part Fire S_P_FIR Failure Arcs(Overvoltage) S_ARC Failure Explosion S_EXP Failure Structural damages S_SD Failure Corrosion S_COR Failure Electric safety issues S_ESI Failure Loss by combustion or destroyed S_LCD Failure 5. ETA 기법적용 콘센트에서발생되는전기적문제는누설전류에의한감전, 접촉불량, 과부하 / 과전류가해당된다. 감전의경우는 2 가닥배선사용 ( 접지선생략 ), 상시전원이인가되어야할장소에잦은누전으로인한누전차단기동작으로상시전원투입이불가하여사용자가접지선절단, 연구기자재의접지설비공사를하지않은경우등의 3 종접지불량에서발생되는문제와누전차단기를설치해야될장소에배선용차단기를설치하여발생된다. 접촉불량과과부하 / 과전류는줄열에의존한다. 사용시간을입력하면높은열이발생됨을알수있다. 고용량부하를지속적으로사용하면콘센트구조체에영향을미치고탄화되어저전류에도화재를일으킨다. 상기와같은문제에대하여 ETA 를통한정성적인분석을실시하였다. Fig. 6 a) 의누설전류 ( 초기사상 ) 가발생했을때전기설비의플래임과연결된 Fig. 5 의 3 종접지 (E3) 를통하여 2 종접지 (E2) 로귀로하게되고최종누전차단기가동작하게된다. 시나리오 ( 결과상황들 ) 1 과 2 의경우는안전하나 3 과 4 의경우는감전이초래된다. 시나리오 2 의경우는접지공사의불량이나누전된기기를발견시에이를개선을통하여안전을확보한다는경우이다. Fig. 6 b) 의접촉불량 ( 초기사상 ) 발생했을때는안전장치가없기때문에전적으로관리자의몫이다. 시나리오 1 의경우는안전하나 2 는화재가발생된다. Fig. 6 c) 의과부하 / 과전류 ( 초기사상 ) 에대한것으로배선용차단기가유일한안전장치인데배선용차단기는단락및정격용량을초과해야동작되는것으로고용량을중첩으로사용시에는동작하겠지만대부분은동작되지않고콘센트에큰에너지가전가된다. Fig. 6 c) 의경우도관리자가전기설비의소비전력확인을통하여체계적인안전관리가가능하다. 시나리오 1 과 2 는안전하나 3 의경우는화재가발생된다. a) initiating event of leakage current (1) 는전류 (A), 은저항 (Ω), t 는시간 (sec) 을나타낸다. 접촉불량은주로콘센트와플러그의접속점에서또는콘센트연결단자부, 플러그연결단자부의불량으로발생하는데국내차단기는이를발견하지못한다. 문제는이런접촉불량발생시정격전류이하의저전류 (5A) 에서도순간 400 이상의높은열이발생되며주위의가연물이있으면바로화재로진전된다 5). 따라서접촉불량에대한안전장치는없다고보면된다. 과부하 / 과전류는한개소에 3 kw이상의소비전력에대하여식 (1) 에서전류는 13.6 A 를입력하고저항과 b) initiating event of poor contact c) initiating event of overload/overcurrent Fig. 6. Analysis of Leakage(E_INT_LEAK), poor contact (IE_ INT_PC) and overcurrent(ie_int_oc) by ETA. 32 J. Korean Soc. Saf., Vol. 32, No. 2, 2017

ETA 를통한연구실험실콘센트회로의전기재해분석 6. 결론 본연구에서는콘센트와연계된전기회로의공사방법불량과사용부주위에대하여현행법, 연구실의실태조사, 감전, 접촉불량, 과부하 / 과전류에대하여 ETA 의정성적분석을통하여그위험성을검증하였다. 본연구에서얻은결론은다음과같다. 1) 콘센트관련구성부품 11 개에대한고장률, 초기사상은내부초기사상 30 개, 외부 11 개로총 41 개구성되어있으며, 결과상황들은전력부분 3 개, 안전부분 12 개로총 15 개로구성하였다. 2) 누설전류 ( 초기사상 ) 에대하여 3 종접지가가장중요한안전장치였으며, 접촉불량의경우는안전장치가없는관계로관리자의철저한점검이필요하다. 과부하 / 과전류의경우는고용량의기기들이연계되었을때는안전장치인배선용차단기가동작되나대부분의경우는이를동작하지않음을확인되었다. 3) 연구실콘센트회로의관리는미래창조과학부는연구실안전점검및정밀안전진단에관한지침을바탕으로하고관리자즉연구자들은소비전력과접지에대하여철저한관리가필요하다. 4) 차후에는본연구에서제시한고장률 (Table 2), 초기사상 (Table 3) 과결과상황들 (Table 4) 을바탕으로사전의위험을발굴하고제거할수있는기법인 FTA (Fault tree analysis) 를이용하여보다객관적인데이터를제시할계획이다. References 1) Korea Institute of Human Resources Development in Science and Technology, Standard Textbook for Safety in Laboratory(Safety for Electricity & Electronics), pp.1, 2015. 2) Korea Electrical Safety Corporation, http://www.kesco.or. kr, Electrical Safety Portal System, Electrical Fire Statics, 2016. 3) S. C. Kim and D. H. Kim, Analysis for the Thermal Properties of the Electrical Wire according to Overload and Disconnection, Jourmal of The Korean Society of Safety, Vol. 22, No 4, pp. 26-31, 2007. 4) S. H. Lee and H. S. Oh, A Study on the Electrical fire Analysis in Overcurrent of Low Voltage Wiring, Journal of the Korean Institute of Illuminating and Electrical installation Engineers Vol. 18, No. 3, pp. 142-148, 2004. 5) S. U. Kang, Analysis of Characteristics and Application of Detecting Sensors for Signals by Poor Contact at Electrical Outlet, Graduate School, Chungbuk National University, pp. 51-59, 2014. 6) S. C. Kim, Analysis of Voltage Drop and Thermal Characteristics for Poor Connections at Electrical Connector of Circuit Breaker of Small Size Pulverizer below 5.5 kw, Journal of the Korean Society of Safety, Vol. 30, No. 3, pp. 26-31, 2015. 7) H. -K. Lim, System Safety Engineering, Hansol Academy, pp.133-137, 2012. 8) National Research Safety Headquarters, Development of Standard Precision Safety Diagnosis Model, pp.14-22, 2016 9) Korea Institute of Human Resources Development in Science and Technology, Standard Textbook for Safety in Laboratory(Safety for Electricity & Electronics), pp.1, 2015. 10) Korea Institute of Human Resources Development in Science and Technology, Standard Textbook for Safety in Laboratory(Safety for Electricity & Electronics), pp.9, 2015. 11) FRONTIS, Introduction of PTC Windchill Quality Solutions, 2016. 12) Korea Electrical Safety Corporation, A Technical Guidebook for Preventing Possible Failures/Accidents based on the Case Studies in a 22.9kV Electrical [6] IEEE gold book, Design of reliable industrial and commercial power systems, pp.259-300, 2007. 13) IEEE Gold Book, Design of Reliable Industrial and Commercial Power Systems, pp.259-300, 2007. 한국안전학회지, 제 32 권제 2 호, 2017 년 33